In general, electrochromic displays are made up of a system comprising a plurality of functional layers. In such displays, the actual electrochromic or coloring layer can consist, for example, of three layers: an ion storage and ion-conducting layer, an electrolyte layer and a layer comprising the actual electrochromic material.
Known electrochromic materials are, for example, PEDOT: PSS (poly(3,4-ethylenedioxythiophene) with PSS (polystyrene sulfonate) providing the counter-ion, or PANI (polyaniline). These materials change color as the result of oxidation or reduction. In electrochromic displays, a controlled reduction or oxidation is achieved by applying a voltage across the electrochromic and ion storage layer. For this reason two electrode layers further need to be provided, between which the color system comprising the electrochromic layer and the ion storage and ion-conducting layer and the electrolyte is provided. More recently, materials that combine the functions of the electrolyte and color system in a single electrochromic layer have also been developed.
The manufacture of an electrochromic display therefore requires manufacturing three layers arranged one on top of another. At least one of the electrode layers must additionally have a transparency of at least about 80% in the visible spectrum so that the color change in the electrochromic layer is visible when voltages are applied and a useable form of display is thus created.
A suitable material has proved to be indium tin oxide (ITO), which is semi-conductive and transparent. Sufficient conductivity is achieved by doping. A transparent electrode layer is then formed by sputtering ITO mixed oxide onto glass or clear transparent film. This transparent layer, which is used as a visible electrode, is then coated with the electrochromic layer and a second electrode by further processes. In the manufacture of the various functional layers, it is particularly disadvantageous to have to combine different process technologies, such as the sputtering of the ITO layer, for example, with printing or gluing processes because this interrupts the production flow.